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27. Which one of the following statements is correct? (1) Electrospray ionization mass spectrum of a compound can be obtained only if it has a net positive charge at pH […]

26. Two homologous proteins were isolated from a psychrophile (P) and a thermophile (T). The purified proteins were subjected to denaturation, protease digestion and circular dichroism (CD). Following observations were […]

25. The structure of a protein is known from X-ray diffraction studies which gave 30% α-helix, 50% β-sheet and 20% random coil. Circular dichroism (CD) measurements gave 50% α-helix, 40% […]

24. The circular dichroism spectrum of a polypeptide composed of 50 amino acids does not show any signal in the region of 185-250 nm. The reason is (1) the polypeptide […]

23. The amino acid alanine has high propensity to occur in helical conformation. The Circular dichroism spectrum of an equimolar mixture of two 20-residue peptides, one composed of only L-alanine […]

22. Which one of the following statements regarding proteins is CORRECT? (1) n → σ* transition requires less energy than n → π* transition and can be monitored by mass […]

21. Denaturation of a highly helical protein having disulfide bridges and two phenylalanines can be monitored as a function of temperature by which one of the following techniques? (1) Recording […]

20. An optical measurement of protein is taken both before and after digestion of the protein by a protease. In which of the following spectroscopic measurement, the signal change, i.e., […]

19. Two 18-residue helical peptides A and B are enantiomers. They can be distinguished by (1) recording their MALDI mass spectrum. (2) hydrolysis followed by amino acid analysis. (3) sequencing […]

18. A and B are two enantiomeric helical peptides. Their chirality can be determined by recording their (1) CD spectrum. (2) UV spectrum. (3) Edman sequencing. (4) Fluorescence spectrum. Why […]